The basic problem of probe testing double-sided ball grid array (BGA) devices is that the double-sided device implementation on the processor board prohibits access by an oscilloscope or other test device of the critical points of the board that require monitoring.
One known prior solution for single unit testing or de-bug testing is to partially depopulate the circuit board by removing SRAMs or other chips one side of the board. This allows access to the testing points, but since the board is only partially functional, the data from the tests on the board does not provide a true and accurate portrayal of the operations of the board. Thus, devices that are BGA mounted, and only single sided, it is possible to merely go to the backside vias and probe those vias to monitor the circuit. But on BGA devices that are double-sided, i.e., have top-side and bottom-side chip entities, there is no known way to probe that type of board while maintaining its full functionality.
Another known prior solution is directed to multi-unit testing or full production testing, and this solution is to install test points on the board. However, the test points would add stubs to the circuit which, in turn, cause reflections in the circuits. Given the number of the BGA entities on the board, and the large number of sample points for each entity, the total number of sample points would be prohibitive. The reflection resulting from the large number of stubs cause degradation in the signals. Moreover, the test points add to the cost and complexity in the manufacturing of the boards.
It is therefore desirable to design a device that would allow for de-bug testing without having to depopulate the boards and could also be used for production testing without causing the reflections in the board circuit and without introducing design changes to the board.